1. Technical Field
The present invention relates generally to currency processing machines, and more specifically to a system and method for detecting optically variable ink on notes by recording images of the notes using multiple modes of illumination that facilitate optimal imaging of specific features.
2. Description of Related Art
Automated, high-volume currency processing is a growing international industry affecting numerous aspects of the distribution, collection, and accounting of paper currency. Currency processing presents unique labor task issues that are intertwined with security considerations. It requires numerous individual tasks, for example: the collection of single notes by a cashier or bank teller, the accounting of individual commercial deposits or bank teller pay-in accounts, the assimilation and shipment of individual deposits or accounts to a central processing facility, the handling and accounting of a currency shipment after it arrives at a processing facility, and the processing of individual accounts through automated processing machines. Any step in the process that can be automated, thereby eliminating the need for a human labor task, saves both the labor requirements for processing currency and increases the security of the entire process. Security is increased when instituting automated processes by eliminating opportunities for theft, inadvertent loss, or mishandling of currency and increasing accounting accuracy.
A highly automated, high-volume processing system is essential to numerous levels of currency distribution and collection networks. Several designs of high-volume processing machines are available in the prior art and used by such varied interests as national central banks, independent currency transporting companies, currency printing facilities, and individual banks. In general, currency processing machines utilize a conveyer system which transports individual notes past a series of detectors. By way of example, a note may be passed through a series of electrical transducers designed to measure the note's width, length, and thickness. The next set of sensors could be optical sensors recording the note's color patterns or serial number. Detectors can likewise be used to detect specific magnetic or other physical characteristics of individual notes.
High volume currency processing machines typically pull individual notes from a stack of currency through a mechanical conveyer past several different detectors in order to facilitate the sorting of the individual notes and the accumulation of data regarding each note fed through the machine. For example, a currency processing machine can perform the simple tasks of processing a stack of currency in order to ensure that it is all of one denomination with proper fitness characteristics while simultaneously counting the stack to confirm a previous accounting. A slightly more complex task of separating a stack of currency into individual denominations while simultaneously counting the currency can be accomplished as well.
On the more complex end of prior art currency processing machines, a stack of currency consisting of various denominations can be fed into the machine for a processing that results in the separation of each denomination, a rejection of any currency that does not meet fitness specifications, the identification of counterfeit bills, and the tracking of individual notes by serial number. The detection of counterfeit bills in particular is an increasingly complex task as the number of anti-counterfeiting features incorporated into currency notes increase both in number and sophistication.
Among the most effect security measures in use are color shifting elements (CSE) such as optical variable ink (OVI), color shifting foils, and similar materials. These elements produce different reflective colors (e.g., magenta and green) at different angles of incidence and reflection. CSEs are widely used security features on major currencies such as the US dollar and the Euro and similar documents. CSEs are typically classified as public security features, meaning they are overt and easily recognizable by the members of the general public upon visual inspection of the note, in contrast to esoteric security features like magnetic strips that are only detected by specialized equipment. Because CSEs such as optically variable inks and foils are considered public security features there are no CSE detectors on high-speed currency sorters.